Modern data communications technologies have greatly expanded the ability to communicate large amounts of data over many types of communications facilities. This explosion in communications capability not only permits the communications of large databases, but has also enabled the digital communications of audio and video content. This high bandwidth communication is now carried out over a variety of facilities, including telephone lines (fiber optic as well as twisted-pair), coaxial cable such as supported by cable television service providers, dedicated network cabling within an office or home location, satellite links, and wireless telephony.
A relatively new technology that has been proposed for data communications is the optical wireless network. According to this approach, data is transmitted by way of modulation of a light beam, in much the same manner as in the case of fiber optic telephone communications. A photoreceiver receives the modulated light, and demodulates the signal to retrieve the data. As opposed to fiber optic-based optical communications, however, this approach does not use a physical cable for transmission of the light signal. In the case of directed optical communications, a line-of-sight relationship between the transmitter and the receiver permits a modulated light beam, such as that produced by a laser, to travel without the waveguide of the fiber optic cable.
Apparatus useful for such communications links is known from U.S. Pat. No. 6,295,154, entitled “Optical Switching Apparatus”, commonly assigned herewith and incorporated herein by reference. This patent discloses a micromirror assembly for directing a light beam in an optical switching apparatus. As disclosed in this patent, the micromirror assembly includes a silicon mirror capable of rotating in two axes which reflects the light beam in a manner that may be precisely controlled by electrical signals. One or more small magnets are attached to the micromirror itself; a set of four coil drivers are arranged in quadrants, and are controlled to attract or repel the micromirror magnets as desired, to tilt the micromirror in the desired direction.
Copending application Ser. No. 90/957,476 which is commonly owned and which is incorporated herein by reference provides a micromirror assembly that includes a package and method for making a package having a sensing capability for the position of the micromirror. This package and method is relatively low-cost, and well suited for high-volume production. The package is molded around a plurality of coil drivers, and their control wiring, for example by injection or transfer molding. A two-axis micromirror and magnet assembly is attached to a shelf overlying the coil drivers. Underlying the mirror is a sensor for sensing the angular position of the mirror. According to the preferred embodiment of the invention, the sensor includes a light-emitting diode and angularly spaced light sensors that can sense the intensity of light emitted by the diode and reflecting from the backside of the mirror. The position of the mirror can be derived from a comparison of the intensities sensed by the various angularly positioned light sensors.
Currently these devices are manually tested which is a time consuming procedure. Performing the necessary tests manually on a single analog micromirror device could take half a day to perform. Now that these micromirror devices will be mass produced to meet the growing demand, there is a need for an automatic test system to test the mass produced devices.